HELP SECTION

CLCOR
Task: This task makes a number of different corrections to a CL
table. These corrections are usually ones that depend on
source or antenna at specific times and so are not suitable for
interpolation between sources (unlike the SN table which is
interpolated to the CL table by CLCAL).
The task copies all records of the input table to the output
table, modifying those selected by the adverbs (sources, time,
subarray, antennas, etc). You are allowed to over-write the
input table, but doing so assumes that there are no problems in
the software, user inputs, or external matters such as electric
power. It is probably best to leave GAINUSE=0. If there is a
sequence of operations to perform, either reset GAINVER for
each step of the sequence or leaver GAINVER also = 0 which uses
the highest version at each step.
Adverbs:
INNAME.....Input UV file name (name). Standard defaults.
INCLASS....Input UV file name (class). Standard defaults.
INSEQ......Input UV file name (seq. #). 0 => highest.
INDISK.....Disk drive # of input UV file. 0 => any.
SOURCES....list of sources to process.
'*' = all; a "-" before a source name
means all except ANY source named.
STOKES.....The desired Stokes to correct.
'R', 'L', 'I', ' '=> all available
FREQID.....Frequency identifier to select (you may determine
which is applicable from the OPTYPE='SCAN' listing
produced by LISTR).
BIF........First IF to process. 0=>all.
EIF........Highest IF to process. 0=>all higher than BIFTIMERANG...Time range of the data to be used. In order:
Start day, hour, min. sec,
end day, hour, min. sec. Days relative to ref.
date.
ANTENNAS...A list of the antennas to be modified. If any
number is negative then all antennas listed are
NOT to be modified. All 0 => use all.
SUBARRAY...The subarray to modify. Do only one at a time.
GAINVER....Input CL table version. If GAINVER is equal zero or
greater than the total number of the CL tables
then GAINVER is equal to the last existing CL table.
GAINUSE....Output CL table version. If GAINUSE not equal GAINVER
(after GAINVER default applied), then a new CL table is
created and the input CL table version (GAINVER) is
copied to version=(high+1). This adverb allows you to
correct a CL table in place or to create a new one, but
not to overwrite an existing one other than the input.
OPCODE.....Operation code (see also EXPLAIN CLCOR):
'POLR' => Modify Right-Left phase difference using
phases in CLCORPRM (deg); up to 20 IFs
may be processed at a time.
'PHAS' => Rotate phase of residual gain by
CLCORPRM (deg); up to 20 IFs may be
processed at a time
'RATE' => Rotate phase of residual gain versus time.
CLCORPRM(1) degrees constant term.
CLCORPRM(2) = rate of change of phase
(degrees/day)
CLCORPRM(3) - (6) = day, hr, min, sec at
which the "zero" phase (CLCORPRM(1)) is
specified.
'OPAC' => apply atmospheric opacity amplitude
corrections using zenith opacity of
CLCORPRM(1) nepers.
'ADEL' => Correct phases, delays and rates for
neutral atmospheric delay.
CLCORPRM(1) = total pressure (mbars) at
station, NOT at sea level.
CLCORPRM(2) = partial pressure of water.
CLCORPRM(3) = Temperature (C)
CLCORPRM(4) = Tropospheric lapse rate
(K/km) (should be negative)
CLCORPRM(5) = Height of tropopause (km)
CLCORPRM(6) = Scale height of water
vapor (km).
'GAIN' => Correct using polynominal gain curve for
antenna ** VOLTAGE** gain as a function of the
zenith angle (ZA) in degrees.
correction = CLCORPRM(1) +
ZA * CLCORPRM(2) +
ZA * ZA * CLCORPRM(3) etc.
'POGN' => Correct using polynominal gain curve for
antenna ** POWER ** gain as a function of the
zenith angle (ZA) in degrees.
correction = CLCORPRM(1) +
ZA * CLCORPRM(2) +
ZA * ZA * CLCORPRM(3) etc.
'CLOC' => Correct residual delay and model parms
for the effects of a linear clock drift
at a particular antenna.
CLCORPRM(1) = rate of change of station
clock (nanosec/day)
CLCORPRM(2) = clock value at the "zero"
time specified by CLCORPRM(3)-(6)
(nanosec)
CLCORPRM(3) - (6) = day, hr, min, sec at
which the "zero" clock (CLCORPRM(2)) is
specified.
CLCORPRM(7) : correction has three modes,
if = 0 then the clock drift is added
as a small correction and CLCORPRM(2)
is ignored.
if = 1 then the total correction set
by the CLCORPRMS is added.
if = 2 then the values present in the
CL table are replaced by those defined
by CLCORPRM(1)-CLCORPRM(6).
'PANG' => Add or remove parallactic angle
corrections from CL table entries.
CLCORPRM(1) > 0 => Add corrections
CLCORPRM(1) =< 0 => Remove corrections
'PONT' => Correct for predictable pointing offset
of an antenna. CLCORPRM(1) is the linear
rate of change of antenna gain as the
pointing drifts.
'IONS' => Make ionospheric Faraday rotation
corrections using one of several models.
CLCORPRM(1) = Model type:
1 = Chiu model, CLCORPRM(3) = Sunspot no.
'ANTP' => Correct antenna and/or source position;
antenna / source corrections are values to be
added to the old positions in meters / sec of arc.
The antenna (only one) must be specified in
the case of antenna correction.
The source (only one) must be specified in
the case of source correction.
!!!!!!!!!!!!!!!!!!! ATTENTION !!!!!!!!!!!!!!!!!!
Starting June 2001 CLCOR corrects the AN or/and
the SU table, if the relevant correction of the
antenna or/and the source is carried out.
So the application of the corrected CL table is
required to match the data.
Once CLCOR has been run, then the CL table must
not be deleted and the correction can be undone
only by doing it again with opposite sign.
If you might forget applying this, then use the
task SPLAT to apply it immediately.
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
1 = "X" correction in meters.
2 = "Y" correction in meters.
3 = "Z" correction in meters.
4 No longer used
5 = Correction in the picture plane towards
the RA direction in sec of arc.
So it is RA correction, multiplied
by COS(DECL).
6 = Declination correction in sec of arc
7 No longer used
8 = drift of the source right ascension in mas/hr
9 = drift of the source declination in mas/hr
The CLCORPRM(8,9) are used if INFILE is 'blank'
'ANTC' => Correct antenna and/or source position; The
same as ANTP except that ANTP corrects the
apparent source position while ANTC corrects
the position of epoch.
'PCAL' => MkIII manual phase cal; replace the gain
correction in the CL table with unit
vectors with phases given in CLCORPRM.
CLCORPRM(1) corresponds to BIF etc.
Phases are given in degrees.
'PCFX' => Patch up missing phase cals. CLCORPRM
gives the expected relationship between
phase cals and uses any non blanked
values.
'SBDL' => Add a delay to the IF residual delays.
Values given in CLCORPRM correspond to
IFs BIF, BIF+1,... EIF in nanosec.
'MBDL' => Change the multiple band delay by
introducing the corresponded slope at
phase vs IF frequency dependence.
Values given in CLCORPRM correspond to
IFs BIF, BIF+1,... EIF in nanosec
'SSLO' => Correct the phase only for an incorrect
frequency used to calculate the phase
at the VLA. CLCORPRM(1) gives the
frequency error in MHz.
'ANAX' => Correct the delay, rate and phase for antenna
axis offset. CLCORPRM is an array of axis
offsets in meters corresponding to the antenna
list given. Note that with 'ANAX' the antenna
table is also modified.
'ATMO' => apply atmospheric and clock delay corrections
using the information for the antennas and
times given in the input file.
The file format:
The first line is number of the data rows.
The remaining lines specify the data with one line
for each antenna/time. Each line is formatted thus:
Column 1: antenna name; The name can be done either
by the antenna number (two digits) or
by the relevant antenna name (two symbols)
Column 2-5: day, hour, min, sec
Column 6: zenith atmosphere delay, in cm
Column 7: clock delay, in cm
Column 8: derivative of the zenith atmosphere
delay, in sec/sec*1.0E14
Column 9: derivative of the clock delay (clock
drift), in sec/sec*1.0E14
For example the following line
1 0 19 1 17.1 9.7327 -11.3983 -4.00728 7.98367
means:
antenna 1; time = 0d 19h 1m 17.1s;
zenith atmosphere delay = 9.7327cm;
clock delay = -11.3983cm;
derivative of the zenith
atmosphere delay =-4.00728E-14sec/sec;
clock drift = 7.98367E-14sec/sec;
If antenna 1 has the relevant name "FD", then
the same line can be given as:
FD 0 19 1 17.1 9.7327 -11.3983 -4.00728 7.98367
This format is in agreement with current July 2008)
DELZN output.
The values of the delays and its derivatives
should correspond to the desired correction.
The corrections for the interferometer delay
and phase are added (with sign) to the relevant
columns of the CL table, which in turn are
added to the data when calibration is applied.
Example 1. The correlator did not provide any
atmosphere correction. Since, the
the atmospheric delays are positive,
the corrections entered in the
INFILE should be negative.
Example 2. The correlator model used 210 cm
for the zenith delay. The true
zenith delay was 220cm. Thus,
CLCOR has to make additional
additive correction of -10cm, and
the INFILE entry should -10cm.
CLCORPRM(1): What correction to make in CL table?
0 => only atmosphere
1 => atmosphere + clocks
'TROP' => Similar to 'ATMO' except the zenith atmospheric
(column 6 in INFILE) is the TOTAL zenith delay,
(typically between 150-400cm). This will be
subtracted from the atmospheric delay applied
by the correlator, which is in the ATMOS column
in the CL table. Make sure there is something
sensible in this column (i.e. loosely between
5-15 nsec) or you will get nonsense. NOTE THAT
EXPERIMENTS CORRELATED BETWEEN NOVEMBER 2002 AND
FEBRUARY 2004 AT THE VLBA CORRELATOR THE ATMOS
COLUMN IN THE CL, MC, AND IM TABLES ARE WRONG, SO
YOU SHOULD NOT USE THIS OPTION.
Other than this 'TROP' runs identically to
'ATMO'
'DISP' => Correction of dispersive delays as a function
of elevation; file contains:
The first line is number of the data rows.
The remaining lines specify the data with one
line for each antenna/time as:
Column 1: antenna number;
Column 2-5: day, hour, min, sec
Column 6: zenith dispersive delay, in 1/cm
Column 7: derivative of the zenith dispersive
delay, in sec/m^2/sec*1.0E14
'SUND' => Correction of the extra time delay caused by
the bending of the light ray passing through the
gravitational field of the solar system planets.
The VLBA correlator (before September 2004)
carries out this correction
considering the source locates at the infinity.
This option removed the correlator correction and
put the correction taking into account the actual
position of the source inside of the solar system.
The correction is carried out only for the one
source (located at the solar system) given at
the adverb SOURCE.
CLCORPRM(1): What correction to make in CL table?
0 => correct actual space craft
position minus infinite position.
The infinite position correction
carried out by correlator is
substituted by actual space craft
position.
1 => correct just actual space
craft position
CLCORPRM(2): Print out the test data?
0 => yes
1 => no
CLCORPRM(3): Print the additional test data?
0 => no:
If CLCORPRM(2) equal 0 then
delays for each antenna/time
are printed out
1 => yes
If CLCORPRM(2) equal 0 then
positions of the spacecraft,
the first planet in the list,
baseline are printed out
additionally
'EOPS' => Correction of UT1-UTC and the Earth's pole
position. The UT1-UTC and the Earth's pole
position need to be corrected if the wrong values
used during correlation.
OPTYPE=EOPS can be used only for data sets with proper
CT tables, namely data from the old VLBA correlator,
DiFX correlators, and, since November 2015, the EVLA.
The INFILE can be picked up from the web side
https://gemini.gsfc.nasa.gov/solve_save/usno_finals.erp
No editing of the file is required.
The actual EOP is interpolated for the time of observation
The default behavior, with CLCORPRM=0, is to use the
same sequence of days (-1,3) as it used at the majority of
cases at the correlator. For special cases (mainly for more
than on day observation), CLCORPRM can be set to
interpolate over a different range of dates.
CLCORPRM(1) Number of days preceding OBSDAT (given in the
data header)
0.0 => 1 (Use 0.1 if you want 0 as
would be appropriate if the first data
start at time ~ 1 day)
CLCORPRM(2) number of days starting from the first
selected day
0.0 => 5
Example CLCORPRM(1)=3, CLCORPRM(2)=7, =>
The first day corresponds to OBSDAT-3 days,
The last day corresponds to OBSDAT+3 days
'IONO' => apply ionosphere and clock delay corrections
using the information for the antennas and
times given in the input file.
Format of data at the input file is identical to
OPCODE = 'ATMO'
The differences with 'ATMO':
1.Phase-delay has the opposite sign
2.Different mapping functions
for 'ATMO'
1/SIN(EL)
for 'IONO'
1/COS(Z_i), where
SIN(Z_i) = (R/(R+h_i)) * COS(EL)
R is the Earth radius
h_i is the ionosphere height
See Thomson, Moran & Swenson 2nd edition
page 560, eq 13.139 and 13.140
CLCORPRM...Parameters: see above.
BADDISK....A list of disks on which scratch files are not to
be placed. This will not affect the output file.
INFILE.....Input file (used for OPCODE = 'ANTP', ANTC', ATMO', 'DISP',
'TROP', 'SUND', 'EOPS')
'ANTP' and 'ANTC'
The first (ascii) data record should specify NLINES,
the number of the lines at the file.
Then, NLINES records must follow in the following format:
Column 1: Julian day
Column 2: right ascension deviation, in mas
Column 3: declination deviation, in mas
The values given at right ascension and declination
deviation correspond to the desired corrections. The
lines must be given in time order. The value added to
CLCORP(5 and 6) for a specific time is determined by
interpolation between the times given in the file. CL
times less than the first get the values of the first
specified time and CL times greater than the last
specified get the values of that last time. Note that
these corrections are in mas at the source and so do not
need a cos(declination) correction.
'ATMO' and 'TROP' and 'IONO'
The first (ascii) data record should specify NLINES,
the number of the lines at the file.
Then, NLINES records must follow in the following format:
Column 1: antenna number; or antenna name
(3 symbols). Antenna name option
is at agreement with the current output
of DELZN
Column 2-5: day, hour, min, sec
Column 6: zenith atmosphere delay, in cm
Column 7: clock delay, in cm
Column 8: derivative of the zenith atmosphere
delay, in sec/sec*1.0E14
Column 9: derivative of the clock delay (clock
drift), in sec/sec*1.0E14
The values given at the atmosphere/clock delay
and their derivatives correspond
to the desired corrections.
'DISP'
The first line is number of the data rows (NLINES)
The remaining lines specify the data with one line for
each antenna/time as:
Column 1: antenna number;
Column 2-5: day, hour, min, sec
Column 6: zenith dispersive delay, in 1/cm
Column 7: derivative of the zenith dispersive
delay, in sec/m^2/sec*1.0E14
'SUND'
The list of the considered planets is given in the input
file. The planets should be chosen from the following
list:
'MERCURY ', 'VENUS ',
'MOON ', 'MARS ',
'JUPITER ', 'SATURN ',
'URANUS ', 'NEPTUNE ',
'PLUTO ', 'SUN '
The INFILE format:
The first line is number of the data rows.
The remaining lines specify the planets list.
Each planet name has to occupy 12 positions:
Example: SUN NEPTUNE MARS
If INFILE .EQ. '', then the only one 'planet':
SUN is selected
'EOPS'
The INFILE can be picked up from the website
https://gemini.gsfc.nasa.gov/solve_save/usno_finals.erp
No editing of the file is required.

EXPLAIN SECTION

CLCOR: Task to apply corrections to a CL table in a variety of ways.
Documentor: W. D. Cotton
Related Programs: LISTR, SPLIT, TABED, LOCIT
This task will compute various corrections and apply them
directly to a calibration (CL) table. The operation to be done
is determined by OPCODE. Details and/or additional information
for the various models is given below.
OPCODE='POLR'
This option causes corrections to be made to remove the
systematic phase offset between the right and left hand polarization
systems. The phase offsets are passed in CLCORPRM in degrees and are
typically determined from running RLDIF (with DOAPPLY and SPECTRAL
false) on polarization calibrated data on a source with known
polarization angle. (NOTE: if RLDIF is run with DOAPPLY true or with
SPECTRAL true, CLCOR should not be used.) Up to 20 IFs specified by
BIF and EIF may be processed in a single run with the corresponding
phase values in CLCORPRM(1) - CLCORPRM(20). Specified phase
corrections are made to the left hand polarization.
Because the feed polarization parameters must be modified as well
as the Calibration table this option will cause the AN table
corresponding to the specified subarray to be modified as well as the
specified CL table. The Q and U values in the SU (source) table
are also modified.
NB: the modification of the CL, SU, and AN tables are cumulative
so a given correction should be made only once for the specific range
of IFs. Thus, if multiple CL tables in the same subarray are to be
corrected OPCODE='PHAS' with STOKES='L' should be used for each range
of IFs for CL tables after the first run with OPCODE='POLR'. (If
the AN table gets messed up, correct all relevant CL tables and then
rerun PCAL; further runs of CLCOR to correct the R-L phase difference
will be unnecessary.)
If PCAL has not been run, CLCOR with OPCODE='POLR' will still
execute but with a stern warning. One should run PCAL first except
for cases with low instrumental polarization on sources of high
intrinsic polarization
OPCODE='PHAS'
This causes the specified phases to be rotated by CLCORPRM(I)
degrees where I = IFnumber - BIF + 1. NOTE: specify either STOKES='R'
or STOKES='L', otherwise the same correction will be applied to the R
and the L polarizations.
OPCODE ='OPAC'
This causes the specified amplitudes to be corrected for
atmospheric opacity using a zenith opacity of CLCORPRM(1)
nepers. This operation does not modify the total model values.
Exact values of the zenith opacity depend on the weather,
especially at higher frequencies, but typical values are given
in the following:
327 Mhz 0.007
610 Mhz 0.007
1.4 GHz 0.008
2.3 GHz 0.01
5.0 GHz 0.01
8.4 GHz 0.01
10 GHz 0.012
15 GHz 0.02
22 GHz 0.05
40 Ghz and up are highly dependent on the weather.
OPCODE='ADEL'
This causes the phases, delays and rates to be corrected
for a model atmosphere. The model used is a two term round
earth approximation. The parameters passed are CLCORPRM(1) the
total atmospheric pressure in millibars at the station, NOT
referred to sea level and CLCORPRM(2), the partial pressure of
water vapor in millibars.
Pressure in mm. of Hg. can be converted to millibars by
multiplying by 1.33322.
Measurements of Dew point can be converted to relative
humidity using the following table:
Relative Humidity ( percent) from temp and DP.
DP depression Dew Point deg C
temp-DP deg C -10 0 10 20 30

0 100 100 100 100 100
1 92 93 94 94 94
2 86 87 88 88 89
3 79 81 82 83 84
4 73 75 77 78 80
5 68 70 72 74 75
6 63 66 68 70 71
7 59 61 63 66 68
8 54 57 60 62 64
9 51 53 56 58 61
10 47 50 53 55 57
12 41 44 47 49
14 35 38 41 44
16 31 34 37 39
18 27 30 33 35
20 24 26 29 32
22 21 23 26
24 18 21 23
26 16 18 21
28 14 16 19
30 12 14 17
The partial pressure of water vapor is obtained by
multiplying the relative humidity (as a fraction) times the
vapor pressure of water obtained from the following table:
Temp (C) Pressure(mbars) Temp (C) Pressure(mbars)
-------- ---------------- --------- ---------------
-40 1.29
-30 3.81 -25 6.35
-20 10.35 -15 16.55
-10 26.00 -5 40.17
0 61.05 5 87.23
10 122.78 15 170.36
20 233.78 25 316.72
30 424.28 35 562.29
40 737.59
Information from Handbook of Physics and Chemistry published
by The Chemical Rubber Co. 46th ed.
The tropospheric lapse rate is the rate at which the
atmosphere cools with increasing height. The model used assumes
that the temperature declines linearly to the tropopause and
then is constant. Accurate values can be derived from
radiosonde data or approximate values can be obtained from the
following table. An accurate value of the height of the
tropopause may be derived from radiosonde data; typical values
can be obtained from the following table (Davis et al. 1985,
Radio Science 20, 1593):
Latitude Lapse rate (K/km) Height of tropopause(km)
30 N -4.7 to -5.9 16
45 N -6.5 11.2
60 N -3.9 8
The scale height of the water vapor may be determined from
radiosonde data (default = 2.2 km).
OPCODE='GAIN'
This causes the specified amplitudes to be corrected by a
factor determined from a polynomial gain curve as a function of
zenith angle (in degrees). The coefficients are specified by
CLCORPRM and up to 20 terms are allowed. This allows for
correction of amplitudes for the zenith angle (i.e. elevation)
dependent behavior of the antenna gain.
The amplitudes are modified by:
FACTOR = CLCORPRM(1) + ZA*CLCORPRM(2) +
ZA*ZA*CLCORPRM(3) ...
OPCODE='CLOC'
This causes the residual delays and model values to be
corrected for a linear clock drift at a particular antenna. The
parameters needed are :
1) clock rate (nanosec/day) ...... CLCORPRM(1)
2) "zero" clock (nanosec) ........ CLCORPRM(2)
3) time of "zero" clock
measurement ........ CLCORPRM(3) -
CLCORPRM(6)
4) correction mode ........ CLCORPRM(7)
if = 0 then the clock drift is added
as a small correction and CLCORPRM(2) is
ignored.
if = 1 then the total correction set
by the CLCORPRMS is added.
if = 2 then the values present in the
CL table are replaced by those defined
by CLCORPRM(1)-CLCORPRM(6).
Mode = 2 gives the user the opportunity to set the
residual delay manually.
OPCODE='PANG'
This option add or removes the phase of the parallactic
angle to/from the residual phases of the specified CL table
entries. The AIPS polarization calibration routines expect
that this correction has NOT been made to the raw data; if the
parallactic angle corrections has been applied, then this
option with CLCORPRM(1) .le. 0 will remove it. The parallactic
angle correction may be added using CLCORPRM(1) .gt. 0.
Note: the above definitions of applying or removing the
parallactic angle correction assumes that the phase of the
first polarization (RCP for VLA, VLBA) decreases with
increasing parallactic angle. This involves the definition of
RCP. If the opposite definition of RCP and LCP is used, then
the sense of applying or removing the parallactic angle
correction given above is removed.
OPCODE='PONT'
This causes the specified amplitudes to be corrected for
any gross predictable pointing error. The antenna gain
correction factor is specified by a time at which the pointing
was set correctly (i.e. the antenna gain is correct) and a
linear drift factor. The TIMERANG parameters define the time at
which pointing was done, CLCORPRM(1) specifies the rate of
change of antenna gain (per hour). The inverse of this will be
applied to the CL gain entries in order to correct the amplitude
error.
OPCODE='IONS'
This option causes ionospheric Faraday rotation
corrections to be computed and applied to the CL table.
Several methods are available for determining the Faraday
rotation correction; the method selected is indicated by the
values given in CLCORPRM.
The group and phase delays introduced by the ionospheric
plasma are also computed and applied to the CL table.
CLCORPRM(1): Electron density model type:
CLCORPRM(1) = 1 => Chiu model.
The electron column density will be computed using a Chiu
model using software provided by Chris Flatters. The model is
described in Chiu, 1975, J. At. Terr Phys. 37, 1563).
CLCORPRM(3) gives the sunspot number.
Sunspot numbers may be obtained from Solar-Geophysical
Data published by NOAA. Daily sunspot numbers are available
and can vary considerably; actual daily sunspot numbers are
preferable to smoothed, averaged or predicted values. The
sunspot number for the day approximately 3 days before the
observation is the appropriate value to use. Moderately
accurate predicted monthly smoothed values are available a
year in advance.
For those who are in a hurry or don't care, the following
table gives observed monthly averaged values until May 1989
followed by the predicted, smoothed values until 1990. The
estimated uncertainty (90 percent) in the smoothed values is given in
parentheses under the predicted value.
International Relative Monthly Sunspot Numbers
Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

1980 164 163 161 159 156 155 153 150 150 150 148 143
1981 140 142 143 143 143 142 140 141 143 142 139 138
1982 137 133 129 124 120 117 115 109 101 96 95 95
1983 93 90 86 82 77 70 66 66 68 68 67 64
1984 60 56 53 50 48 46 44 40 34 29 25 22
1985 20 20 19 18 18 18 17 17 17 17 17 15
1986 14 13 13 14 14 14 14 13 12 13 15 16
1987 18 20 22 24 26 28 31 35 39 44 47 51
1988 58 65 71 78 84 94 104 114 121 125 130 138
1989 142 145 150 153 157 163 166 169 176 181 183 185
( 5)(11)(16)(19)(21)(23)(24)
1990 186 187 185 180 174 170 168 166 159 151 144 139
(26)(29)(31)(32)(31)(28)(27)(29)(30)(31)(29)(26)
1991 138 134 130 129 130 128 124 119 114 113 115 115
(27)(28)(29)(34)(35)(32)(29)(26)(22)(20)(21)(24)
OPCODE='ANTP', 'ANTC'
This option will correct phases for an incorrect antenna and
source position; delays and rates are also corrected. The corrections
to be added to the old values for the x,y, and z components are given
in meters as CLCORPRM(1), CLCORPRM(2) and CLCORPRM(3). If the
coordinates are in a right handed system then CLCORPRM(4) should be
1.0 or larger.
The corrections to be added to the source position at the picture
plane are given in sec of arc as CLCORPRM(5) for RA direction and
as CLCORPRM(6) for declination. OPCODE 'ANTP' adds the corrections to
the apparent positions and recomputes the positions of epoch, 'ANTC'
does the reverse.
Note: only one FQ ID is processed per run; if there are several FQ
ID then CLCOR must be run several times.
A correction for antenna position errors should be made before
further calibration is done. First, run CLCOR with OPCODE='ANTP'
using GAINVER=1; GAINUSE=2 to copy CL table 1 to version 2 and then
correcting for the antenna position error(s). Then run CALIB applying
CL table 2 (DOCAL=1; GAINUSE=2). Use SNPLT to examine the results to
be sure that the correction was done properly. When using CLCAL the
input CL table should be version 2 (GAINVER=2). If there are adequate
observations of calibrators then LOCIT can be used to determine
antenna position errors.
OPCODE='PCAL'
This option allows entering complex gain corrections
directly into the CL table. This operation is mostly of use in
the setting of MkIII VLBI manual phase cals so only the phase
can be specified. If the amplitudes also should be changed then
TABED can be used to multiply the real and imaginary parts of
the complex gains by the appropriate value.
Note: the phases in the CL table are corrections to be
added to the data and thus have the opposite sign from the
Haystack convention. Up to 20 IFs can be entered with
CLCORPRM(1) corresponding to IF BIF, CLCORPRM(2) to BIF+1 etc.
Phases are given in degrees.
Note: for some reason phase cals read by AIPS are 144
degrees more positive that those decoded by the Haystack
software. To obtain the desired results add 144 degrees to any
manual phase cals used in the Haystack system.
OPCODE='PCFX'
This option is similar to 'PCAL' except that any unblanked
phases are left unchanged. Any blanked phases are replaced by
the value expected based on any unblanked phases and the
relationship between the IF given in CLCORPRM. In the case that
all phases are blanked then this option is the same as 'PCAL'.
This option is intended for use when some phase cals are
present for a given antenna but are missing for some IFs. This
option allows using the good values and estimating the missing
values.
OPCODE='SBDL'
This option allows adding values to the IF residual delays.
This correction will not effect the current values of the total
model delay and is intended primarily for correcting MkIII data
for the antenna based difference between the multi-band and
single-band delays. Individual IF values can be entered but it
is usually assumed in the MkIII system that this is a constant
value for all IF. In this case fill CLCORPRM with the desired
correction. Values are given in nanoseconds and will be added
to the current correction, i.e. subtracted from the data when
this table is applied. The values in CLCORPRM correspond to IFs
BIF, BIF+1, ... EIF.
Having applied this correction the new CL table application
will change the slope of phase frequency dependence inside
the each IF. The change of the slope at each IF is determined
by the value of corresponded parameter CLCORPRM(I). This option
does not change the phase difference between different IF's.
OPCODE='MBDL'
This option changes the multiple band delay by introducing
the corresponded slope at phase vs frequency dependence. The same
phase is added for all channels of the given IF. Values of
CLCORPRM are given at nanoseconds. The added phase is determined
by the next formula FI[I]=TWOPI*CLCORPRM[I]*DF[I], where DF[I]
is a difference between the frequency of the given IF and
residual one. The values of multiple band delays CLCORPRM[I] can
be different for different IF, although it is constant typically.
The values CLCORPRM[I] for all IF have to be installed even if
they are the same for the all IF.
The delay corresponded to the first IF - CLCORPRM[1] is substituted
at the modified CL table at MBDELAY1(2) column.
OPCODE='SSLO'
The VLA has four separate 'IFs'. In normal observing, the
frequencies of these are locked together into pairs. Each pair forms
an AIPS IF. In normal observing, the phase calculation, or fringe
stopping, is done correctly.
However, for some spectral line observing, it is desirable to
have the separate VLA IFs of a pair at the same center frequency, but
with different bandwidths. In this case, the Signed Sum of the LOs is
different and the two frequencies cannot be locked together. The VLA
has only sufficient hardware to control one IF of each pair, so the
fringes for the other cannot be stopped correctly. In general, this
leads to decorrelation. However, if the frequency difference is
sufficiently small, it is merely results in a residual phase error,
which changes slowly with time.
This option is to allow a post facto correction to be made
to the phase only. Note that the delay is calculated correctly.
The VLA IFs that are affected are 'B' and 'C'. By convention,
'A' and 'D' are always fringe-stopped correctly.
Since the error depends upon the antenna location, the
possibility that the antenna coordinates are defined in a left-
handed system is allowed for, even though the VLA uses a right-
handed system.
The correction for SSLO is calculated at each CL table entry
time as follows:
If A is the antenna position vector and S is the unit
source position vector, then the calculated phase correction
(dph) is
dph = 2 * pi * [ integer part of ( A . S * dfq / c)]
where dfq is the frequency correction in Hz calculated from
CLCORPRM(1).
The new value of the complex gain in the CL table (gnew) is
calculated from the old value (gold) as:
gnew = gold * exp (i * dph)
or, in Cartesian coordinates:
xnew = xold * cos(dph) - yold * sin(dph)
ynew = xold * sin(dph) + yold * cos(dph)
where g = x + i * y
OPCODE='ANAX'
This option changes the delay, rate and phase in accordance
with an antenna axis offset. CLCORPRM(I, I=1, NANTSL) is the
axis offset of antenna I in meters. The AN table is modified
also. Three types of antenna mount (alt-azimuth (and Nasmyth), XY-EW,
and equatorial) are supported.